Process for catalytic hydrogenation of adiponitrile



3,272,867 PROCESS FOR CATALYTIC HYDROGENATION OF ADIPONITRILE John W.Conner, Phillip W. Evans, Albert J. Isacks, Jr.,

and Chester P. Neiswender, Jrz, Pensacola, Fla., assignors to MonsantoCompany, a corporation of Delaware No Drawing. Filed Apr. 3, 1963, Ser.No. 270,161 5 Claims. (Cl. 260583) This invention relates to an improvedcatalytic hydrogenation process and more particularly to an improvementin the preparation of hexamethylenediamine by the hydrogenation ofadiponitrile in the presence of a catalyst with improved service life.

Hexamethylenediamine is an important intermediate for the synthesis ofpolyamides and polyester amides, and its preparation has been thesubject of many investigations. A successful and reasonably efiicientmethod for commercial preparation of hexamethylenediamine is by thehydrogenation of adiponitrile in the presence of ammonia and either anickel or cobalt catalyst. This process may be carried out either on abatch or continuous basis. The batch method may comprise suspending anickel or cobalt catalyst in a liquid medium containing the material tobe hydrogenated and agitating the mixture with hydrogen gas until therequired quantity of hydrogen has been absorbed. This batchwise methodof hydrogenation has the advantage that sutficient time may be allowedfor the process to reach any desired stage of completion and thedisadvantage that the process is discontinuous and hence more costlythan if the equipment for the hydrogenation were kept in constant use.

The continuous process, which is in much greater commercial favor, maycomprise bringing a heated fluid mixture of essentially ammonia,hydrogen, and adiponitrile into contact with a stationary solidhydrogenation catalyst. The ammonia and the adiponitrile may beco-mingled at first and the mixture allowed to mix with a stream ofhydrogen en route to the catalyst chamber or separate streams of theindividual reactants may be allowed to converge in any manner suitablefor obtaining the proper proportions of the individual reactants.

Although many improvements have been etfected in commercial continuoushydrogenation processes for the production of hexamethylenediamine, eventhe most sophisticated of these processes must be terminated at sometime because of detrimental reduction or loss in the ability of thecatalyst to aid or effect the required hydrogenation. This loss incatalyst activity occurs, regardless of hydrogenation operatingtemperature, at some point of time in the operation of the processdependent upon the operating conditions for the process and the amountof material which has been hydrogenated by given catalyst as well asother factors. Although it is known to vary the hydrogenationtemperature and pressure and to use catalyst additives to increase theyield of hydrogenated material from a given quantity of catalyst none ofthese methods is completely successful either singly or in combination.

An object of this invention, therefore, is to preparehexamethylenediamine by catalytically hydrogenating adiponitrile by animproved process.

Another object is to provide an improved process for the preparation ofhexamethylenediamine by the catalytic hydrogenation of adiponitrile withminimum formation of by-products and maximum yields.

Another object is to provide an improved process for hydrogenatingadiponitrile to hexamethylenediamine in the presence of a catalysthaving improved yield and service life.

Still another object is to provide a method of prepara- United StatesPatent 0 3,272,867 Patented Sept. 13, 1966 tion of a hydrogenationcatalyst having improved service life and activity.

A still further object is to provide an improved hydrogenation catalysthaving increased service life and activity.

These and other objects of this invention will be apparent from thedescription hereinafter.

In accordance with this invention it has been discovered that the aboveand other objects are accomplished by hydrogenating adiponitrile undercontrolled conditions of temperature and pressure in the presence ofammonia and at least one of tre group of nonmagnetic catalystscomprising nickel and cobalt.

The terms magnetic and nonmagnetic as used in this specification arerelative and in all instances, except those otherwise specified,magnetic is used to describe materials which exhibit ferromagneticproperties when subjected to a magnetic field of an intensity to bedescribed later, and nonmagnetic is used to describe materials whichfail to exhibit ferromagnetic properties when subjected to a magneticfield of an intensity to be described later.

In a particularly preferred embodiment of the invention, a mixturecomprising at least adiponitrile, ammonia, and hydrogen is contactedwith a nonmagnetic cobalt catalyst under conditions of elevatedtemperature and pressure to produce crude hexamethylenediamine in a highyield and containing a minimum of hydrogenation by-products.

The hydrogenation process of this invention may be performed either at abatch or continuous process, and the hydrogenation reactants, heattransfer compounds, if any, and any hydrogenation by-product suppressantor catalyst activator compounds or mixtures which may be used, may becontacted with the nonmagnetic catalyst and with each other in theliquid phase, the vapor phase, or combinations thereof depending uponthe hydrogenation reactants and the desired conditions of temperatureand pressure for hydrogenation.

The hydrogenation reactants, the ammonia, and any by-product suppressantor catalyst activator compounds or mixtures which may be used may be fedseparately to the nonmagnetic catalyst for contacting or any two or moreof the above mentioned components may be mixed with each other prior totheir contact with the catalyst. In the preferred example of thehydrogenation of adiponitrile to hexamethylenediamine in the presence ofa nonmagnetic cobalt catalyst, it has been found advantageous to mix theadiponitrile and the ammonia and any byproduct suppressant compounds orcatalyst promotors prior to the contacting of the mixture with thehydrogen and the nonmagnetic catalyst. Water may be present in minorconcentrations in one or more of the compounds of the hydrogenationprocess feed stream or streams to the nonmagnetic cobalt catalystwithout affecting the beneficial results of improved catalyst activityobtained by this invention.

The adiponitrile which may be employed in the process of this inventionmay be obtained from any suitable source such as the reaction of adipicacid with ammonia, the reaction of dichlorobutane with hydrogen cyanide,the hydrogenation of dicyanobutene, or other known means for thepreparation thereof and should be of the degree of purity well known inthe art.

The ammonia and hydrogen which may be employed in the practice of thisinvention may be obtained from any suitable source and also should be ofthe degree of purity well known in the art.

The temperature employed for the hydrogenation reaction may be between25 C. and 200 C., and the hydrogen pressure used may be maintainedbetween 25 and 10,000 pounds per square inch or higher. In the practiceof the invention, it is preferred generally to carry out thehydrogenation at the lowest temperature and hydrogen pressure at whichhydrogen is absorbed at a reasonably rapid rate. In the preferredexample, the hydrogenation reaction temperature may be between 120 C.and 170 C., and the hydrogen pressure may be between 4,000 and 6,000pounds per square inch.

A hydrogenation catalyst suitable for the practice of this invention maybe prepared from cobalt or nickel catalytic materials and is obtainedpreferably in a finely divided form. The catalytic materials may bedeposited on a porous supporting means such as pumice, kieselguhr,alumina gel, and silica gel. Catalyst may be prepared conveniently foruse in the hydrogenation process by compressing the catalyst powdersinto pellets or briquettes, sintering the pellets or briquettes in afurnace, separating the sintered catalyst pellets or briquettes into amagnetic portion and a nonmagnetic portion, and then reducing thenonmagnetic portion thereof in a stream of hydrogen gas prior to thecontacting with the hydrogenation reactants. In the preferred example,nonmagnetic cobalt catalyst pellets may be prepared from the pure oxideof the cobalt metal which may be derived by precipitation of thecarbonate of the metal from a nitrate solution thereof with ammonia andcarbon dioxide or with ammonium carbonate. The precipitated carbonate ofthe metal may then be decomposed to the oxide by roasting in air at atemperature between 300 C. and 500 C. In general, the lowest possibleroasting temperature should be used to obtain the most satisfactorysintered catalyst.

The resulting oxide, in the presence or absence of the metal, then maybe kneaded in a suitable kneading machin to improve its densitycharacteristics, and the thus kneaded oxide is combined with from 1% toand preferably from 2% to 4% of a lubricant and sintering aid.

Generally, the lubricants and sintering aids are solids at normal roomtemperatures which melt below the sintering temperature causing thegranules of catalyst during the sintering to occupy a smaller space thanthe nonsintered catalyst and are substantially completely vaporizable atthe temperature of sintering leaving practically no ash after sintering.Especially effective lubricants and sintering aids are the animal andvegetable stearins and normally higher fatty acids such as those acidscontaining more than 12 carbon atoms and including tridecylic, myristic,pentadecylic, and more particularly .palmitic and stearic acids oresters thereof. The esters are preferably those which are solids at roomtemperature but are fluid at temperatures below the sinteringtemperature of the metal oxide and examples of such esters are theglycolic, glyceryl, and similar polyhydric alcohol esters of the acidssuch as glyceryl tristearate and glyceryl tripalmitate, whether of themono or polycarboxylate types. The simple esters such as methyl, ethyl,propyl, and higher monohydric alcohol esters may be used, however, withresults not as outstanding.

After the sintering aid is thoroughly distributed throughout thecatalyst, the resulting mixture then may be pilled or formed intopellets by any suitable means. One such means is a Stokes rotarypelleting machine.

The pelleted mixture of catalyst and sintering aid is then heated in asuitable sintering furnace in an oxidizing atmosphere at a temperaturebetween 500 C. and 1100 C., and preferably between 700 C. and 1100 C. Ina preferred example of cobalt catalyst in the form of cylindrical pillshaving a diameter of about 0.25 inch and a height of about 0.25 inch,the proper sintering may take from 2 to 4 hours.

After the sintering operation, the catalyst pills are cooled slowly to aroom temperature for subsequent separation into a magnetic andnon-magnetic portion. In the example of the catalyst pellets describedabove, this cooling or annealing operation may take about 8 hours.

The cool sintered cobalt catalyst pellets may be separated into activenonmagnetic and inactive magnetic portions by either batch or continuousmethods, using any suitable means such as a magnetic separator. Themagnetic separator used may be either of the permanent magnet orelectromagnetic type, well known in the art; and the most well knowntypes of magnetic separators include the magnetic pulley, suspendedseparation magnets, spout type, drum type, and gravity inductionseparators. Of these types, the magnetic pulley type with either anelectromagnetic or permanent magnet pulley is perhaps most easilyapplied to this invention. In the separation of the inactive magneticcatalyst pellets from the active nonmagnetic catalyst pellets, thestrength of the magnetic field, the size of the air gaps in the magneticcircuit, and the time the pellets are in the magnetic field arevariables which may be pertinent to obtaining a nonmagnetic portion ofcatalyst pellets which has optimum activity and service life.

The strength of the magnetic field for the separation of the sinteredcatalyst pellets into magnetic and nonmagnetic portions may be between200 and 10,000 gauss; however, this field intensity may be greater,depending upon the type of magnetic separator used. In a typical exampleof the separation of sintered cobalt catalyst pellets of the typedescribed above, a magnetic pulley separator having a permanent magnetwith a field intensity of 500 to 2,000 gauss may be used to give goodseparation of the inactive magnetic portion from the active nonmagneticcobalt catalyst pellets.

It is clear to those skilled in the art that the diameter of themagnetic pulley and the speed of the endless conveyor tbelt travelingaround the magnetic pulley may be varied, dependent upon the fieldintensity of the magnetic pulley, to obtain good separation of thenonmagnetic active catalyst pellets. In general, the rate at which thecatalyst pellets may be separated, the feed rate of the endless belt inthe case of a magnetic pulley separator, increases with the diameter ofthe magnetic pulley being used, and at field intensities between 200 and10,000 gauss, the speed of the endless belt may be between 1 and 400feet per minute for magnetic pulley diameters between 4 and 48 inches.

. The size of the air gap in the magnetic circuit and duration of thecatalyst pellets in the magnetic field may be varied dependent upon thetype of magnetic separator used and the field intensity of the magnetused therein. In general, to obtain good separation of the magnetic andnonmagnetic portions of the catalyst pellets, the air gap permitted inthe magnetic circuit varies inversely with the intensity of the magneticfield and directly with the period of time of the catalyst pelletswithin the magnetic field.

The following examples will further and more specifically illustrate thenature of the present invention and in what manner the same can becarried out in practice, but it should be understood that the inventionis not limited to the said examples.

EXAMPLE I Sintered cobalt oxide catalyst pellets in the shape ofcylindrical pills having a diameter of about 0.25 inch and a height ofabout 0.25 inch, prepared in a manner well known in the art, wereseparated into a magnetic and a nonmagnetic portion on a batch basisusing a permanent magnet having field intensity of approximately 600gauss by passing the permanent magnet over a stationary horizontal bedapproximately 4 inch thick of the sintered cobalt catalyst pellets at aheight of approximately 0 to 3 inches. The catalyst pellets, as theyadhered to the magnet, were removed from the face thereof and collectedas the magnetic portion. This procedure was continued until noadditional pellets were collected on the face of the magnet. Thecatalyst pellets remaining in the horizontal bed were collected as thenonmagnetic portion.

Forty (40) grams of the nonmagnetic cobalt oxide catalyst pellets thusobtained were charged to a standard laboratory Shaker bomb having a 1400cc. volume. Two hundred sixteen (216) grams of adiponitrile and 150grams of anhydrous ammonia were charged to the bomb and then thetemperature was raised to 150 C. This mixture of catalyst, adiponitrile,and ammonia was pressured to 4500 pounds per square inch gauge withhydrogen gas while maintaining the temperature therein at 150 C. Therate at which the hydrogen pressure decreased was recorded as a measureof the activity of a catalyst contained in the apparatus and the resultsof 7 test runs and a standard unseparated catalyst run made in anidentical manner to that described above are shown in Table 1 below.

Table 1 Rate of decrease of hydrogen In all instances it was found thatthe rate at which the hydrogen pressure within the Shaker bomb decreased.was at least 5%, and generally to greater than that obtained for asintered cobalt catalyst prepared and tested in an identical manner butnot separated into magnetic and nonmagnetic portions.

7 EXAMPLE ll Sintered cobalt oxide pellets, cylindrical in shape andhaving a diameter of 0.25 inch and a length of 0. 25 inch, were preparedin a manner well known in the art and separated into nonmagnetic andmagnetic portions on a magnetic pulley separator comprising an endlessbelt traveling at 69 feet per minute concentrically with a permanentmagnetic pulley 8 inches in diameter and having a magnetic field on thebelt surface of 500 to 2,000 gauss intensity. Operation of the magneticpulley separator in this manner gave a yield of 78% nonmagnetic catalystand 22% magnetic catalyst. Nonmagnetic catalyst thus obtained wascharged to standard catalyst cartridges used in the commercialcontinuous process for the synthesis of hexamethylenediamine by thehydrogenation of adiponitrile. A substantially identical amount ofunseparated catalyst, i.e., mixed magnetic and nonmagnetic sinteredcobalt catalyst pellets, were charged to the cartridges of asubstantially identical commercial unit for the continuous synthesis ofhexamethylenediamine by the hydrogenation of adiponitrile. These twocommercial hydrogenation units were operated at substantially the sameconditions of temperature and pressure for a three-months period withthe amount of adiponitrile being fed to the units being varied to obtainsubstantially identical yields of hexamethylenediamine from eachcommercial unit. In each instance when a loss of catalyst activitynecessitated the termination of the run, the catalysts were regeneratedwith hydrogen in a substantially identical manner. The number of runsmade using the comparison catalyst cartridges thus made and the amountsof adiponitrile fed to each commercial unit are shown in Table 2 below.

Nonmagnetic sintered cobalt catalyst prepared in the manner described inExample 11 was prepared and charged to catalyst cartridges of 5commercial continuous synthe sis units for the production ofvhexamethylenediamirie by the hydrogenation of adiponitrile, and thethroughput of adiponitrile per catalyst cartridge was measured for eachcartridge for 12 runs. Results of these tests are shown in Table 3below.

Table 3.-Thr0 ughput of Adiponitrile in 1,000 Pounds N onmagnetiesintered Cobalt Catalyst Type Cartridge No 1 2 3 4 5 As can be seen fromthe table above, the amount of adiponitrile charged to each catalystcartridge averaged 185,200 :pounds per run made. This average feed rateper cartridge of adiponitrile showed a 19% increase over the averagefeed rate of adiponitrile to commercial synthesis units operated undersubstantially identical conditions during the same period and containingsintered cobalt catalyst pellets not separated into magnetic andnonmagnetic portions.

The nonmagnetic catalyst of this invention may be prepared and used inways other than those set forth in the foregoing description andexamples. For certain operating conditions, the catalyst may besupported by a suitable carrier such as silica gel, kieselguhr,diatomaceous earth, clay, bauxite, and the like. The nonmagneticcatalyst also may be combined with or used in conjunction with othercatalyst or catalysts, as desired.

The nonmagnetic catalyst also may be used in other than a fixed bedarrangement. It may be prepared in small particles adapted to bemaintained in a state of agitation by passage of the reactants and/orthe reaction products therethrough, and alternately, it ,may besuspended in the liquids, gases, or vapors during the reaction, beingseparated therefrom and returned to the reaction zone.

Although the theory of the above described invention is not clearlyunderstood, the advantages thereof are obvious to those skilled in theart. As can be seen clearly, by the simple expedient of separating andremoving the magnetic portion of the catalyst from the catalyst mass byeconomical and uncomplicated methods, an active nonmagnetic catalystresults having an overall activity and service life increased by atleast 15% or more, depending upon the operating conditions chosen forthe hexamethylenedia-mine synthesis reaction. This major increasesubstantially offsets minimal losses of the catalyst itself resultingfrom the separation. Further, no changes are necessary to existinghexamet-hylenediamine synthesis equipment to obtain the beneficialresults of this invention.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that we do not limit ourselves to the specific embodimentsthereof except as defined in the appended claims.

What is claimed is:

1. A process for oatalytically hydrogenating adiponitrile to producehexamethylenediamine comprising contacting, at a temperature between 25C. and 200 C. and at a pressure between 25 and 10,000 pounds per squareinch, a mixture comprising adiponitrile, ammonia, and hydrogen withhydrogenation catalyst selected from the group consisting of cobalt andnickel prepared from a corresponding oxide, said oxide havingnonmagnetic properties when subjected to a magnetic field of intensitybetween 200 gauss and 10,000 gauss.

2. The process of claim 1 wherein the temperature is between 120 C. and170 C.

3. The process of claim 1 wherein the pressure is between 4000 and 6000pounds per square inch.

4. The process of claim 1 wherein the temperature is between 120 C. and170 C. and the pressure is between 4000 and 6000 pounds per square inch.

References Cited by the Examiner UNITED STATES PATENTS 2,166,150 7/1939HoWk 260583 2,225,059 12/1940 Lazier 260583 2,677,668 5/1954 Ahlberg252472 2,707,706 5/1955 Bauch 252472 CHARLES B. PARKER, PrimaryExaminer.

ANTON H. SUTTO, RICHARD L. RAYMOND,

Assistant Examiners.

1. A PROCESS FOR CATALYRICALLY HYDROGENATING ADIPONITRILE TO PRODUCEHEXAMETHYLENEDIAMINE COMPRISING CONTACTING, AT A TEMPERATURE BETWEEN25*C. AND 200*C. AND AT A PRESSURE BETWEEN 25 AND 10,000 POUNDS PERSQUARE INCH, A MIXTURE COMPRISING ADIPONITRILE, AMMONIA, AND HYDROGENWITH HYDROGENATION CATALYST SELECTED FROM THE GROUP CONSISTING OF COBALTAND NICKEL PREPARED FROM A CORRESPONDING OXIDE, SAID OXIDE HAVINGNONMAGNETIC PROPERTIES WHEN SUBJECT TO A MAGNETIC FIELD OF INTENSITYBETWEEN 200 GAUSS AND 10,000 GAUSS.